Fragile X syndrome (FXS) is the most common inherited form of intellectual disability. The typical male has an IQ of 50 to 55. Some are severely affected (low IQ, nonverbal), while others are mildly affected (mild intellectual disabiliy, can read, very sociable). Females are generally less affected than males but have an even broader range in function. A few females have severe intellectual and adaptive impairments, but most have a normal or borderline intellectual ability; about one-third have mild cognitive impairment. This wide range in cognitive ability almost certainly leads to variable ability to make choices and live independently. This application focuses on a particular form of choice making-decisional capacity-the ability to make a meaningful decision about whether to participate in research. Individuals with FXS have served as participants in research studies for more than 30 years. For the most part, this research has been relatively noninvasive, limited to parent surveys and neuropsychological or psycho-educational assessments. Some studies have drawn blood, collected saliva, measured heart rate, or used neuroimaging, but until recently there has been a paucity of treatment research. This scenario has changed dramatically in the last 3 years. Advances in understanding the molecular basis of FXS have led to a new generation of targeted treatment approaches, and clinical trials are underway using a variety of compounds. The possibility of side effects and the potential for significant changes in behavior and learning abilty elevate to a new level the importance of obtaining meaningful consent. Researchers and IRB members need data to help guide decisions about involving individuals with FXS in the consent process. Only a few studies have investigated decisional capacity of individuals with intellectual and developmental disabilities, and none have studied individuals with FXS. Virtually nothing is known about the extent to which individuals with FXS are involved in decisions about research participation, and no studies have investigated decisional capacity in FXS. This project will assess the range of decisional capacity in FXS, identify factors associated with variability in decisional capacity, and develop and evaluate a tablet-based decision aid to assist in obtaining informed consent. The study team includes experts in FXS, human research protection professionals, specialists in developing materials for informed decision making, a leading researcher in FXS clinical trials, and researchers who have developed and evaluated gold-standard measures for characterizing decisional capacity. The study will provide important information about the nature of decisional capacity in FXS and will provide guidance for researchers, IRB members, and pharmaceutical companies seeking to include individuals with FXS as study participants.